Marble landscape chips stained by mildew

Q: We have a 2-foot border of marble chips around our house. On the backside of the house, the marble chips have become tarnished to a dark brown by mold and mildew. Tilex seems to kill the mold/mildew, but doesn’t return the color. Obviously, I can’t clean each individual stone by hand. Are there any products or methods available to kill the mold/mildew and return the marble chips to their original white luster? Thanks. —Bob G. in West Virginia

A: You could have a tough job ahead, because you just might have to clean each stone by hand. However, before we go to that extreme, let’s try a couple of other tricks first.

A bathroom tile cleaner may not be the best thing for cleaning marble. As you mentioned, the cleaner killed the mold and mildew but didn’t get rid of the tarnish. The next step is to test a few different cleaners on one or two of the marble chips to see what the results are.

•Put away the name-brand cleaner (which may contribute to the staining problem rather than solve it) and pick up some plain old Borax, a stain fighter and fungicide (and a heckuva pest-control solution, but that’s for another column).

•Mix the powder with water at the ratio recommended on the package and sponge it onto one of the stained marble chips. Let it sit for about 10 minutes, then rinse the stone. Do the same with a half-and-half solution of vinegar and water, and then a one-third to two-thirds solution of bleach and water.

Let the chips dry and note the results.

If you find a good solution, apply it either by hand with a thick sponge (wear rubber gloves to protect your skin) and rinse with a garden hose, or look into renting a pressure washer and spraying on the solution at low pressure and then rinsing it off at a higher pressure to speed up the job.

Professional marble cleaners are also available at home-improvement and flooring stores. These will cost more than the household solutions and may only be applicable by hand, but if nothing else works, these may do the trick — remove the mildew and restore the color.